The invention relates to a locking device for a switchable valve drive component, with a first locking body and a second locking body that can be brought into engagement with each other or can be brought out of engagement with each other in order to couple or uncouple two components that are arranged movably with respect to one another, wherein at least one of the two locking bodies has at least one curved surface.
Switchable valve train components, such as switchable cam followers, switchable rocker arms, switchable finger levers, or switchable tappets, are used as cam followers in internal combustion engines in order to reduce the fuel consumption and pollutant emissions. For this purpose, switchable cam followers allow, under certain operating situations, a switching between different stroke curves that are transmitted from different cams of a camshaft to one or more valves, or a temporary complete shutdown of one or more cylinders. For such valve train components, a locking device enables the fixed connection or the detachment of actuation-relevant individual parts of these same components.
A locking device of such a valve train component is formed of a locking element, for example, a piston that can be actuated in a mechanical-hydraulic way and can be spring-mounted, as well as a holder, for example, a hole, with which the piston is brought into engagement or brought out of engagement as necessary, in order to couple or decouple two components, for example, rocker arms, which move in a pivoting or linear motion relative to each other.
For known locking devices, the locking partners each have a circular cross-section with essentially uniform radius, wherein the radius of the piston is necessarily somewhat smaller than the radius of the holder for the piston. In this way, in the locked state, a linear contact with only one contact line in the longitudinal direction is produced on the locking contact surfaces. Such locking devices therefore have relatively poor osculation of the locking partners and therefore comparatively high bearing pressure. The wear is high accordingly due to the locking and unlocking that occurs frequently during operation. Independent of an actuating device and the size of the radii of the locking device, an imprecise alignment of the piston in the holder in the horizontal direction or an imprecise crown position of the piston is also produced, from which a disadvantageous variance in the locking play of the locking device is produced.
For other known locking devices, the two locking partners each have a rectangular profile. The bearing pressure is indeed usually low for these locking elements, but the production requires relatively high processing costs.
U.S. Pat. No. 5,544,626 A shows a two-part switchable cam follower in which, between two longitudinal bars of a box-shaped first arm, a second arm is installed so that it can pivot relative to the first arm. The two arms can be locked to each other by a piston installed in the longitudinal direction of the cam follower. The piston has a circular cross-section and is supported so that it can move longitudinally in a hole of the first arm with a similarly circular cross-section. The piston has a flattened axial end piece that can be brought into engagement in a positive locking arrangement with a flat bottom side of the second arm for locking the cam follower.
DE 10 2005 048 951 A1 shows a two-part switchable cam follower with a larger outer lever with respect to an opposing rotational axis and a smaller inner lever, wherein the inner lever can pivot relative to the outer lever. The two levers can be locked with each other by a locking pin. The locking pin is held in the longitudinal direction in the outer lever and is supported so that it can move longitudinally and can be brought into engagement with the inner lever. The locking pin is actuated in a mechanical-hydraulic way, in order to lock the outer lever rigidly to the inner lever as needed.
From DE 10 2010 026 360 A1, a tappet for a valve train is known in which, in a window of a housing, there is an anti-rotation securing device projecting past the outer lateral surface of the housing. The housing is held in a guide hole of a surrounding construction not described in more detail. The guide hole has a partial cylindrical axial guide in cross-section, in which the anti-rotation securing device engages. The anti-rotation securing device is constructed as a finger-like, perpendicular half-cylindrical body with a relatively small cylindrical height in which the lateral surface nestles only partially against the axial guide and is not forced, so that an approximately point-shaped contact is produced between the anti-rotation securing device and a wall of the axial guide. The lateral surface of the anti-rotation securing device describes, in cross-section, a round taper formed of two circular arcs, a so-called gothic profile, wherein the tip of the round taper is replaced by a flattened section. Every possible contact point between the gothic profiled anti-rotation securing device and the partial cylindrical axial guide is due to the gothic profile spaced apart from the edge of the guide hole of the housing at which the anti-rotation securing device is especially at risk of wear.